Recently, as a working fluid for a heat cycle system such as a refrigerant for a refrigerator, a refrigerant for an air-conditioning apparatus, a working fluid for a power generation system (such as an exhaust heat recovery power generation), a working fluid for a latent heat transport apparatus (such as a heat pipe), or a secondary cooling medium, expectations are concentrated on hydrofluoroolefin (HFO), namely, hydrofluorocarbon (HFC) having a carbon-carbon double bond. HFO attracts attention as a working fluid having less effect on the ozone layer and less effect on global warming since the carbon-carbon double bond is likely to be decomposed by OH radicals in the air.
As a working fluid having not only less effect on the ozone layer and global warming but also low combustibility, there are hydrochlorofluoroolefin (HCFO) such as hydrochlorofluoropropene and chlorofluoroolefin (CFO) having a high ratio of halogen which reduces combustibility and having a carbon-carbon double bond which is likely to be decomposed by OH radicals in the air. Further, as one kind of hydrochlorofluoropropene, there is known 1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd).
In the present specification, regarding halogenated hydrocarbon, an abbreviated name of the compound is mentioned in parentheses behind a compound name, and the abbreviated name is used instead of the compound name according to need. Further, only numeric characters and small characters of alphabet behind a hyphen (-) (“1224yd” in “HCFO-1224yd”, for example) are sometimes used as the abbreviated name.
Note that in 1224yd, a Z-isomer and an E-isomer which are geometric isomers exist according to positions of substituents bonded to carbon having a double bond. When the compound name or the abbreviated name of the compound is used unless otherwise stated regarding the compound such as 1224yd with respect to which the Z-isomer and the E-isomer exist in the present specification, the Z-isomer, the E-isomer, or a mixture having an arbitrary ratio of the Z-isomer and the E-isomer is indicated. When (Z) or (E) is denoted behind the compound name or the abbreviated name of the compound, a Z-isomer or an E-isomer of each compound is indicated.
It is known that 1224yd can be obtained as an intermediate in a process of manufacturing 2,3,3,3-tetrafluoropropene (1234yf) which has been greatly expected as a new refrigerant in recent years from 1,1-dichloro-2,3,3,3-tetrafluoropropene (1214ya).
Specifically, there has been conventionally known a method of manufacturing 1214ya in a manner that 1,1-dichloro-2,2,3,3,3-pentafluoropropane (225ca) or the like is used as a raw material, and is subjected to a dehydrofluorination reaction in an alkaline aqueous solution in the presence of a phase-transfer catalyst or through a gas phase reaction in the presence of a catalyst such as chromium, iron, copper, or activated carbon, and the obtained 1214ya is reduced by using hydrogen in the presence of a catalyst, to be converted into 1234yf. Besides, as an intermediate in this reduction reaction, 1224yd can be obtained. Further, in this reduction reaction, a lot of kinds of fluorine-containing compounds are generated as by-products, other than 1224yd.
Here, 1224yd being the intermediate can be separated from 1214ya being an unreacted raw material and 1234yf being an object, through normal distillation, but, a fraction obtained by this distillation operation contains, other than 1224yd, 1-chloro-1,2,2,3,3,3-hexafluoropropane (226ca), 1-chloro-1,1,2,2,3,3-hexafluoropropane (226cb), 1-chloro-1,3,3,3-tetrafluoropropene (1224zb), and 2-chloro-1,3,3,3-tetrafluoropropene (1224xe) being by-products of the reduction reaction described above.
As a method of separating the by-products from the composition containing such by-products (referred to as “1224yd composition”, hereinafter), distillation can be considered, and a compound such as the aforementioned 226ca has a boiling point close to a boiling point of 1224yd (a boiling point of 1224yd (Z) is 15° C., and a boiling point of 1224yd (E) is 19° C.). Further, the above-described compound forms an azeotropic composition or an azeotropic-like composition with 1224yd, so that it is not easy to separate the above-described compound from the 1224yd composition. Specifically, when a composition containing 1224yd at a high concentration is tried to be obtained from the 1224yd composition through a normal distillation method, a distillation apparatus with a very large number of stages is required, so that generally, it has been difficult to perform the separation through the distillation.
As a method of separating a composition which is difficult to be separated through normal distillation, there has been conventionally known an extractive distillation method in which a solvent having an affinity to a partial component contained in a composition is brought into contact with the composition to perform distillation (refer to Patent Reference 1 (JP-A No. H09-020765), for example). However, it has been unknown and also it has been difficult to predict that what kind of solvent is used to obtain the composition containing 1224yd at a high concentration by separating the by-products from the 1224yd composition efficiently, for example, in a distillation column with a small number of stages.
Further, 1224yd (Z) has chemical stability higher than that of 1224yd (E), and thus is a compound which is more preferable to be used as a working fluid for a heat cycle, however, an operation in which the composition containing 1224yd (Z) at a high concentration is obtained by separating only 1224yd (Z) from the 1224yd composition has not been conducted.